With regards to Shem's anti clone points.
If learning is based on knowledge and practice, and a clone has the memories of Starkiller, it's entirely plausible that he could raplidly develop his Force potential and moves to become just as strong as Galen was when he was cloned. As for memories beyond the cloning point, we have Force Connections etc.

The only thing I have trouble with is so far, rapid cloning requires Force-canceling Ysalamiri, which create Force "blind" clones, who can't feel the Force at all.

If alchemy, I don't see any Sith at the time of the films being capable of alchemy, save perhaps Palpatine, who wouldn't have any motive for doing so, that could involve Vader. It was Palpatine's attempts to use Galen to kill Vader that opened Vader's eyes to the traitorous nature of Palpatine. It was at this point that he began training his own apprentices to defeat his Master, so he wouldn't plan to clone Marek, a potential replacement, for Palpatine.